Good morning all, this is my first post so hopefully it is entered into the right category given the nature of the query.

This query relates to constructing an outbuilding under permitted development within the curtilage of my property. I have read the technical guidance relating to permitted development and the extract of the latest 2015 Act as I was trying to maximise my allowance without falling foul of the rules.

The ground level had changed at one end of the proposed outbuilding around 7-8 years ago. The level was raised by 200mm due to a new hard standing being built over the original grass level. I my opinion this wasn't an engineering operation but feel free to disagree if this could be reasonably objected (if indeed it makes any difference to the main question that is looming!)

I was not entirely sure if this 'new' level was a suitable datum point to use for measuring the height of the outbuilding. The Act only states to use the highest adjacent ground level, and I was of the hopeful opinion that this would be measured at the time of 'prior to the construction of the proposed outbuilding' - a term I've seen quoted while searching for an answer. Obviously re-engineering the ground level immediately prior to construction would (and should not) be permitted to achieve a new ground level, and would be taken as part of the construction works in effect.

I therefore applied to the council for clarification on the matter by way of a 'Planning Enquiry Form'. The council's answer to the ground level was that the raised area was not deemed a suitable reference point. When I pushed the for more clarification they could indeed see from google map searches that the raised area had been added around 7 years ago. Furthermore they also said the whole area of rear garden had probably been engineered during the construction of the dwelling (and neighbourhood) to a higher level, and that they would interpret natural ground level to be the lay of the ground prior to the construction of my property (the estate was built in the 60's). It should be noted I have had permission refused for a pitched roof outbuilding on the same plot to this new proposal, mainly due to objections from a neighbour and the council agreeing with them despite various amendments to lessen the impact. I feel the council is just getting daft in it's replies as we haven't seen eye to eye on the previous proposal.

I have no idea what the ground level was prior to the construction of the neighbourhood and can't imagine many people would know this. The council said it could look into archive files held on 'microfische', but only if someone objected to the building or if I applied for a Lawful Development Certificate. To me using this point in time is bizarre and I can't find any case law that defines the time used to reference 'Natural Ground Level'. Usually if there is no definition a method is adopted as what the term would mean to the average lay person.

So after a lot of babbling the questions are: A) Does anyone know of any case law that clarifies the point in time? B) Why on Earth would the original lay of the land be appropriate now, given that the neighbouring properties were all built together and the ground levels 'neutralised'? (the neighbours garden is the same level as mine).C) If the council looked into the original land and found that my properties surrounding ground level had actually been lowered, say, out of a hill of around 10 metres, would this give me a total permitted development of 12.5metres relative to the post construction levels of the original house? (I think I know the answer to this one, but it proves how silly the concept is).

Thanks for reading, and if you can offer advice it would be appreciated.